1. Field of the Invention
This invention relates generally to the field of mechanisms for allowing remote control to occur between host computers and a plurality of mass storage business continuance volumes and more particularly to cascading commands for issuance by a host system to collect information about and transmit control commands to volumes at one or more levels away from the host in the system.
2. Background
Mass storage systems have become increasingly cost effective for critical business systems. Advances such as Redundant Arrays of Independent Disks (RAID) technologies and Hierarchical Storage Management (HSM) systems have greatly improved the reliability of mass storage by providing a number of different redundancy features. Additionally, HSM systems such as the SYMMETRIX(trademark) systems that are commercially available from the Assignee of the subject application provide disaster recovery facilities such as Symmetrix Remote Data Facilities (SFDF). These allow a SYMMETRIX(trademark) 5xxx system located at one site to maintain a continuous copy or mirror of the data at the logical volume level in other SYMMETRIX(trademark) systems located in physically separate sites. FIG. 7a (Prior Art) illustrates a redundancy technique used in SYMMETRIX(trademark) systems to provide mirroring, RAID configurations, and other forms of redundant disk storage. As seen in FIG. 7a (Prior Art) disk adapters DA1, DA2 and DA3 are connected over small computer storage interface (SCSI) buses to physical disk drives C, such as C1, C2 and C3 on disk adapter DA1. In SYMMETRIX(trademark) systems, in some implementations, a physical disk C1 is divided into three logical disks, called H1, H2, and H3.
To illustrate this, assume a typical physical disk connected to a mainframe computer contains 2000 cylinders. In an HSM system such as SYMMETRIX(trademark) systems, shown in FIG. 7a (Prior Art) using disks C which are larger in capacity than the typical disks, the larger disks C can be logically divided into smaller logical units. If the disks C in this example hold 6000 cylinders, this physical disk C has the capacity of three typical disks. Each logical disk H, in this example, would be the equivalent of one typical disk.
Still in FIG. 7a (Prior Art), if a typical disk contains a single large file or dataset named DSN1, mirroring redundancy techniques used in an HSM such as SYMMETRIX(trademark) systems, can create copies of this dataset DSN1 on disk adapters DA2 and DA3. In the example here, the first standard copy of DSN1 is physically located on disk adapter DA1, disk C1, at logical disk H2. The first mirror copy, DSN1M1 is located physically on disk adapter DA2, at physical disk C2, logical disk H1. The second mirror copy DSN1M2 is located on disk adapter DA3, physical disk C3, logical disk H3.
In FIG. 7b (Prior Art), a more abstract way of thinking about mirroring or redundancy is shown. If the HSM system allows three mirrors for a standard disk, the HSM might have disks configured as shown herexe2x80x94the standard disk for data DSN1, is allocated to disk adapter DA1, physical disk C1. The first mirror, Mirror1, is assigned to disk adapter DA2, physical disk C3, and so on. In SYMMETRIX(trademark) systems, the combination of disk adapter DA, physical disk C and logical disk H, is resolved into a SYMMETRIX(trademark) device number. In this example, the SYMMETRIX(trademark) system synchronizes the mirrors in a transparent manner. When the data from disk adapter DA1, physical disk C1 has been copied to mirror1 and mirror 2, the devices are considered synchronized.
Now turning to FIG. 7c (Prior Art), disk adapters DA are shown as they might be configured in Symmetrix Remote Data Facilities (SRDF) systems for disaster recovery. As seen in FIG. 7C (Prior Art), a SYMMETRIX A(MASTER) system has been configured in a unidirectional SRDF campus solution with SYMMETRIX B(SLAVE) system.
When the SRDF features are used, a SYMMETRIX(trademark) system includes not only cache memory, channel directors CD and disk adapters DA, but remote link directors RLD. Within each SYMMETRIX(trademark) unit, three volume types may be defined: local (L), source (R1) and target (R2). Local volumes L are volumes unique to that SYMMETRIX(trademark) unit. They are only accessible to hosts attached to that SYMMETRIX(trademark) unit (in this example, HOST 1.)
Still in FIG. 7c (Prior Art), source volumes R1 are logical volumes that reside on a SYMMETRIX(trademark) unit with the SRDF features activated, so that the data on source volumes R1 is mirrored or copied to respective target volumes R2 on another SYMMETRIX(trademark) unit (in this example, HOST 2). The target volumes R2 are located on one or more separate SYMMETRIX(trademark) units in an SRDF configuration.
As seen in FIG. 7c (Prior Art), a path is established by the remote link directors RLD to allow data to be mirrored. The paths shown here are labeled remote access group 0, or RA0.
Turning now to FIG. 7d (Prior Art), a bidirectional SRDF configuration is shown. Host 1 is logically in communication with standard volume std, in this example. As mentioned above, SYMMETRIX(trademark) systems would normally (in the absence of SRDF features) establish some mirroring for an ordinary volume. In this case, mirrors M1 and M2 in SYMMETRIX(trademark) A might be established for standard volume std. The SRDF feature takes this mirroring one step further. Instead of creating a mirror of SRDF standard source volume R1 on SYMMETRIX(trademark) A, the SRDF features, using the remote link directors RLD, assign a remote mirror M1 in SYMMETRIX(trademark) B. In other words, source volumes R1 are standard volumes that reside on a SYMMETRIX(trademark) unit, with the data on those volumes mirrored to respective target R2 volumes on another SYMMETRIX(trademark) unit, here SYMMETRIX(trademark) B. If the source volume R1 fails, the SYMMETRIX(trademark) A will transparently access the data on the corresponding target volume R2 in SYMMETRIX(trademark) B. When the failing volume is replaced, the remotely mirrored pair is re-synchronized automatically as a background operation, using the data in the target volume R2.
Still in FIG. 7d (Prior Art), target R2 volumes are a copy of the source R1 volumes in another SYMMETRIX(trademark) unit. A target volume R2, typically has a default configuration mode of xe2x80x9cread-onlyxe2x80x9d to any host with access to the SYMMETRIX(trademark) unit in which it resides. In this example, mirror M1, in SYMMETRIX(trademark) B, which is the remote mirror to the source volume R1 in SYMMETRIX(trademark) A, would be made xe2x80x9cnot-ready""xe2x80x9d to Host 2. Normally, writes to the target volume R2 on Host 2, occur via the link paths created by the remote link director. However, if the source volume R1 on SYMMETRIX(trademark) A fails, SYMMETRIX(trademark) A will transparently access the data on its corresponding target R2 volume (here, M1 in SYMMETRIX(trademark) B)
A target volume R2 typically has a default configuration mode of xe2x80x9cread-onlyxe2x80x9d to any host with access to its SYMMETRIX(trademark) unit, in this example, HOST 2. To enable disaster recovery, the remote link directors RLD in a SYMMETRIX(trademark) unit, create link paths RA0 with the SYMMETRIX(trademark) unit containing the target volumes R2. As data is written to a source volume R1 by HOST 1, the remote link director RLD in SYMMETRIX(trademark) A automatically writes a copy of that data over link path RA0 of the SRDF connection to the corresponding target volume R2 on the designated SYMMETRIX B system. Thus, if a source volume R1 fails for any reason, the remote link director RLD will transparently access the data on the corresponding target volume R2 on the designated target SYMMETRIX B system over the link paths RA0 and transmit that to HOST 1.
New writes to the failed source volume R1 in SYMMETRIX(trademark) A accumulate as invalid tracks in the cache of SYMMETRIX(trademark) Axe2x80x94the unit containing the source volume R1. When the failing source volume R1 is replaced, the remotely mirrored pair is re-synchronized automatically as a background operation within the SYMMETRIX(trademark) unit, using the data in the appropriate target volume R2.
FIG. 8 (Prior Art) shows an extended distance implementation of the SRDF features. So far, the above discussion dealt primarily with an SRDF CAMPUS connection, which usually involves physical proximity, such as units located in two buildings on a college campus. In extended distance configuration shown in FIG. 8 (Prior Art), the source volume R1 on SYMMETRIX(trademark) unit SYMMETRIX A is being automatically and transparently copied to target volume R2 on SYMMETRIX C over the SRDF EXTENDED DISTANCE connection. The SRDF EXTENDED DISTANCE solution allows source volume R1 to be automatically copied to target volume R2 on SYMMETRIX C, which may be located thousands of miles away. Thus, if a disaster such as a flood destroys all the hosts and SYMMETRIX(trademark) units located at a campus site, the application can still be run from the remote, extended distance site represented here by SYMMETRIX C. Sites can be as much as 37.5 miles (60 km) apart from each other in a xe2x80x9ccampusxe2x80x9d solution, or in an extended distance solution over 37.5 miles (60 km) apart using T3 or E3 or similar high speed links.
These disaster recovery remote sites, whether campus or extended ones, are mirrors or copies of data stored on the SYMMETRIX(trademark) systems physically located near the host computer. As described above, the copying is done by the respective SYMMETRIX(trademark) systems automatically, once all appropriate SYMMETRIX(trademark) systems have been configured for the SRDF feature. This means the host(s) and local SYMMETRIX(trademark) systems at each site are able to operate as efficiently as if the remote copying were not occurring. That is, the continuous copying to the remote sites is not xe2x80x9clogically visiblexe2x80x9d to the host computers at the various sites, nor does it interfere with processing at the host. Hence, a host computer, is not able to send commands that effect changes to the remote sites. This is true even if the remote sites are located only one step away in a campus solution. If the host wishes to effect changes, either the CAMPUS or the extended sites, there was heretofore no way of doing this directly at the local site.
It is an object of this invention to enable a host computer to cause volumes to be managed remotely.
It is another object of the present invention to enable a host computer to issue commands to effect changes in volumes at remote SRDF sites.
Still another object of the present invention is to enable a host computer to collect information about volumes at remote SRDF sites.
These and other objects are achieved by a host system for remote control of mass storage volumes using cascading commands which collect information indirectly about a stream of linked volumes attached to mass storage volumes attached to other hosts or located at physically separate sites. A host computer program issues the cascading commands which ask the locally communicating mass storage system to return information which can be used to identify one or more levels of remote mass storage systems. Once a mass storage system at a given level has been identified, commands can be sent by the host through the locally communicating mass storage system to cause actions to occur at the identified remote level, whether or not there are multiple intervening levels of remote mass storage systems. In the embodiment shown, a host computer can query, establish, split, re-establish, copy and restore business continuance volumes at any level in a chain of local and remote mass storage system sites. Those skilled in the art will appreciate that other commands could be implemented as well to effect changes in the volumes at remote sites.
It is an aspect of the present invention that it enables host commands to cascade over one or more intervening levels of mass storage systems at remote sites to take effect at a particular designated site.
Still another aspect of the present invention is that it enables a host to monitor the operations being controlled at the designated remote site.
Still another aspect of the present invention is that it can significantly improve the remote site""s ability to be effective as a business continuance site for disaster recovery.